Magnetic compass



March 5, 1963 w. E. HULL 3,079,698

- MAGNETIC COMPASS Filed April 29, 1957 V Sheets-Sheet l grwwnm WALTL R E. HULL March 5, 1963 w. E. HULL MAGNETIC COMPASS 4 Sheets-Sheet 2 Filed April 29, 1957 W WALTER E. HULL March 5, 1963 w. E. HULL MAGNETIC COMPASS 4 Sheets-Sheet 3 Filed April 29, 1957 INVENTOR. HALTER E. HULL A rramvsy March 5, 1963 w. E. HULL MAGNETIC COMPASS 4 Sheets-Sheet 4 Filed April 29, 1957 3m w g 2 n H m m5 NR Nm/W m NZ QNI I) TTORNE) United States Patent 3,il79,693 MAGNETE (JOMPASS Walter E. Hull, RD. 13, Gortland, Ohio Filed Apr. 29, 1957, Ser. No. 655,757 3 Claims. (Qt. 33-223) The present invention relates to compasses, more particularly to magnetic compasses of the type suitable for use in boats, aircraft, motor vehicles and the like, and the principal object of the invention is to provide new and improved compasses of the character described.

This application is a continuation-in-part of my copending application for Letters Patent entitled Magnetic Compass Serial Number 565,629, filed February 15, 1956, now Letters Patent 2,943,398.

in compasses of the type herein contemplated, there has been a long standing problem of providing for expansion and contraction of the dampening liquid which is contained within a sealed housing and in which the indicating member is immersed. Some prior art constructions ernploy a metal diaphragm which forms a part of the housing wall and which flexes to permit expansion and contraction of the liquid. Such constructions have not been entirely satisfactory because of the difiiculty of obtaining a permanent, leakproor' seal between the housing and the diaphragm.

Other prior art constructions contemplate only partially filling the housing with dampening liquid to thereby provide an air space which contracts and expands in volume inversely with expansion and contraction of the dampening liquid. This construction, while satisfactory in operation, is not satisfactory from a sales standpoint since, during handling of the compass prior to installation, the free air bubble may easily be seen. Most customers, seeing this bubble, will assume that some of the dampening liquid has escaped from the casing and while such is not necessarily the case, a sales person must take the time to assure the customer that such bubble is perfectly normal. The necessity of a technical explanation of the phenomenon, if indeed the sales person can give a satisfactory explanation and if the customer believes it, is a decided disadvantage of these prior art constructions.

The present invention provides a simplified compass construction which provides for expansion and contraction of the dampening liquid without danger of leakage and without having a free air bubble within the housing with the disadvantages aforesaid. These and other advantages will readily become apparent from a study of the following description and from the drawings appended thereto.

In the drawings accompanying this specification and forming a part of this application there is shown, for purpose of illustration, embodiments which the invention may assume, and in these drawings:

FIGURE 1 is a front elevational view of an embodiment of the improved compass,

FIGURE 2 is an enlarged, side elevational view thereof, the near side of the outer casing being removed and certain parts being shown in section to illustrate the interior construction,

FIGURE 3 is a sectional view of a detail prior to assembly,

FlGURE 4 is a perspective view of two details prior to their assembly with each other,

FIGURE 5 is a perspective view of another detail,

FIGURE 6 is an enlarged, fragmentary sectional view of still another detail,

FIGURE 7 is a view similar to FIGURE 2 but of another embodiment of the invention and with the outer casing and its associated parts omitted in the interest of simplicity,

FIGURE 8 is a perspective view of a detail employed in the embodiment illustrated in FIGURE 7,

FIGURES 9, l0 and 11 illustrate the manner in which the detail shown in FIGURE 8 is made,

FIGURE 12 is a plan view of the detail shown in FIG- URE 8 drawn to the same scale as FIGURE 9,

FIGURE 13 is a plan view of another detail employed in the embodiment illustrated in FIGURE 7, and

FIGURE 14 is a view similar to FIGURE 7 but of still another embodiment.

With reference to FiuURES 1 and 2, the present invention comprises an outer casing 10 of plastic or the like which encloses the about to be described compass mechanism. To facilitate assembly of the various parts, it is preferable to form the casing to provide a front portion 11 and a rear portion 12 which are adapted to be secured together by screws or the like, not shown.

Positioned substantially centrally of casing 1% is an assembly which comprises a housing 13 in which a compass card 14 is rotatably mounted. The front portion 15 of housing 13 is rounded at 16 and at least this portion of the housing is transparent so that the compass card may be seen and read through the housing wall. Front portion 11 of casing 1 1 is apertured at 17 to provide a window through which the front portion of housing 13 is visible. As will be apparent, rounded portion 16 of housing portion 15 magnifies compass card 14 and makes it appear larger, thus making the compass easier to read.

In the present embodiment and as seen in FIGURE 2, housing 13 rests upon an opaque plate 1%. A light bulb Trill, carried by a suitable socket 162 which is in turn carried by the rear portion 12 of outer casing 10, is positioned beneath plate 169. At the present time, one or more suitable apertures 103 are formed in plate 169 to permit light from bulb 101 to escape to the interior of housing 13 so as to illuminate the compass card 14. in order to provide a desirable soft lighting effect on the compass card, aperture 1'83 is disposed adjacent the front wall i=5 of the housing 13 intermediate the periphery of the compass card and the periphery of the housing so as to illuminate that portion of the compass card visible through the housing wall 16.

Compass card 14 is conventional in that it comprises an inverted cup of non-magnetic material having a central epending stud 18 (see FIGURE 3) whose lower end tapers to a point to provide a low friction pivot. Card 14 has the usual magnets 1? secured thereto for making it responsive to the earths magnetic lines of force and the exterior of the card carries the usual indicia.

As in conventional constructions, stud 13 rests in a concavity formed in the upper surface of a jewel 2b which is secured inside a sleeve 21. The lower end of sleeve 21 is soldered or otherwise secured to an upstanding portion 22 of a supporting member 23 which is non-magnetic and preferably somewhat resilient.

in the present embodiment, supporting member 23 has a lower portion 24 which extends transversely of portion 22, an upper portion 25 which lies in substantially the same plane as portion 24, and an intermediate connecting portion 25. In the position of parts shown in full lines in FIGURE 3, portion 25 of supporting member 23 is spaced apart sufiiciently from portion 24 so that the compass card may be assembled, as shown, with the supporting member. However, as will later be disclosed, subsequent assembly operations will spring portion 25' and maintain it in the dot-dash line position to prevent disassembly between the compass cord and the supporting member. As will be understood, portion 26 serves not only to connect portions 24, 25, but also serves as a lubber line.

As heretofore disclosed, compass card 14 is encased in ahousing vl3. This housing is preferably substantially flat on top and bottomand as best seen in 'FIGUREA, comprises the previously mentioned front portion 15 together with a rear portion 27. As will appear, these portions are adapted to be fused together to form the complete housing. The inside or housing portion 1 5 is formed to provide spaced, inwardly directed respective upper and lower grooves 28 and 29 for receiving the support ing member 23.

To assemble compass card 14am supporting member 23 with housingportion 15,"and after compass card stud 18 has been inserted in sleeve 21 to rest upon' jewel 29, supporting member portion 25 will be sprung to its dotdash line position shown in FIGURE 3 and the assembly then slid into housing portion 15 with member portion 26 foremost. As indicated, supporting member portion 24 will he slid into groove 29 while portion 25 will he 'slid into groove 28. It is to be understood that the spacing between grooves 23, 29 is such that supporting member portion will .be held in the dot-dash line position shown in FIGURE 3 and in the full line position shown in FIGURE 2, to prevent disassembly of the compass card from the supporting member. The resiliency of the supporting member will tightly wedge the latter and the housing portion 15 together against unintentional disassembly as will be clear.

As inconventional constructions, housing 13 is adapted to be filled with a suitable liquid to dampen oscillatory movement of the compass card, and since the housing is sealed, means must be provided to permit expansion and contraction of the dampening liquid resulting from temperature variations. The present invention provides a highly effective, low cost construction for accommodation of this expansion and contraction and such construction possesses none of the disadvantages of the prior are constructions as hereinabove pointed out.

The present invention is similar to one of the previous y mentioned prior art constructions in that it provides a bubble of air or other compressible fluid within the housing; however, this bubble is trapped within the housing and is hidden from View regardless of the position in which the assembled compass is held. Briefly, the bubble is 'encassed in a transparent, flexible envelope which is permanently secured in a predetermined position with-in the housing.

As best seen in FIGURES'2 and 5, a thin, preferably transparent membrane 30 of a suitable plastic or the like (which is, of course, insoluble in the dampening liquid) encloses the bubble. In the present embodiment, membrane 30 is cemented to the exterior of a thin, preferably transparent body 31 which is configurated similar to housing portion '27 but which is smaller so as to fit therewithin. In order to maintain body 31 in position, it is formed with a plurality of cars 32 (herein shown to be four in number) which engage the interior of housing portion 27 and which also engage respective lugs 33 which project from the interior of the curved side walls and from the fiat, top and bottom walls of this housing portion. Under certain circumstances, it may be desirable to cement or otherwise secure membrane 30 directly to the interior of the housing portion.

With the support member and the compass card as 'sembly positioned in housing portion 15 and with body 31 positioned in housing portion 27, faces 34 of the housing portions will be sealed together. In the present embodiment, one or both faces 34 will be moistened with a suitable liquid which softens the material. The faces will then be pressed together and held until the liquid evaporates thus leaving the two housing portions fused together into an integral, leak-proof unit. Obviously, instead era softening liquid, the two housing portions may be secured together by means of a suitable cement. 'It will be seen in FIGURE 2 that after assembly, supporting member 23 engages body 31 and prevents shifting thereof within the housing. ,I I

Withh'ousing portions 15, 27 fused or otherwise secured together, the completed housing will be filled with the usual dampening liquid through an aperture 35 formedin housing portion 27. It isto be understood that it is important the interior of the housing be completely filled and that no free air bubble be entrapped therein because a free air bubble would create the impression that some of the dampening liquid had escaped from the housing.

As illustrated in FIGURE 2, aperture 35 in housing 13 is adapted to be closed by means of a cap 36 which overlies aperture .35 and which is preferably formed of substantially the same material as is housing portion 27. Referring to FIGURE 6, the underside of cap '36 is adapted to be moistened with a suitable softening liquid which may be similar to that used in fusing housing por tions 15, 27 together. The cap will then be pressed against the exterior of housing portion 27, so as to overlie aperture 25, until the softening liquid evaporates to thercupon fuse cap 36 to the housing and provide aleak-proof joint therebetween.

In order to insure that no air bubbles will be trapped beneath cap 36 the cap is provided with a taperedprojection which fits within aperture 35. -As the cap is positioned in place, the projection will displace a quantity of liquid from the housing to insure that no air is entrapped beneath the cap. Further, projection 37, as it enters the aperture, insures that cap 36 properly 'positioned overlying the aperture;

It should be pointed out that a more dependable closure is obtained by fusing cap 36 to the exterior of the housing than be wedging a plug into the aperture as has been done in prior art devices. With the present construct-ion,- shrinkage of the housing in the cap will not result in leak age since any stresses imposed by such shrinkage will be spread over a relatively large area thus reducing the possibility of separation between the housing and the cap which would result in leakage of the dampening liquid from the housing.

With housing 13 assembled as heretofore described, a workable, accurate compass is provided. However, this compass would be accurate only whenu's'ed in a locality free of local magnetic fields. In the event the compass is used in an automobile or aircraft or the 1ike,'it is necessary to provide means for neutralizing the effect of such local field on the compass in order to permit it to read accurately.

Neutralization of these local magnetic field's is accomplished by means of suitable compensating devices which "are adjusted to set up a counter magnetic field which is, in its effect on the compass card, equal to and in the op posite direction to the local field. These compensating devices are contained within casing 10 and are indicated generally by the reference character 38 and since they are the subject of my co pending application for Letters Patent herein above mentioned and form no part of the present invention, they will not herein further be described.

FIGURE 7 illustrates another embodiment of the invention, si'rnil'ar parts being identified by the same ref erence charactersheretofore used but with the suflix a added. In this embodiment, the means employed to pro- 'vide for expansion and contraction of the dampening liquid comprises a generally kidney-shaped container or bag 39 (see FIGURE 8) which is disposed within housing 13a and maintained in predetermined position'therein by means later to be disclosed. Bag 39'is preferably formed from thin, flexible plastic material which is both impervious to the passage of air therethrough and insoluble in the dampening liquid and comprises two pieces of thin plastic sealed together along their margins and providing an air space therebetween. As above mentioned, bag 39 is preferably kidney-shaped so that it may easily be flexed, to fit within the housing without interfering with the com- .P se r U. V V.

' t the present time, bag 39 is formed by passing a .pair of ribbons of plastic material, disposed in overlying fe la?- so /aces a tion, between respective lower and upper die members 40 and 41 (see FIGURES 9, and 11). Lower die member 49 is preferably flat while upper die member 41 has a kidney-shaped recess 42 in its lower face which is in communication with a vacuum pump or the like (not shown) via a passage 43.

With the die members separated and with respective plastic ribbons adjacent respective adjoining die faces, air will be evacuated from recess 42 to thus cause the upper plastic ribbon to conform to the upper die face. A suitable solvent, or cement, will be applied at 4"; to the undersurface of the upper plastic ribbon adjacent to and margining the recess 42. The die members will then be brought together (see FIGURE 11) to permanently seal the two ribbons together at the place where the solvent was applied. The die members will now be separated, the ribbons moved longitudinally to position unsealed portions between the dies and the foregoing operation repeated. It will be understood that the ribbons emerge from the dies sealed together to provide a series of plastic bubbles which will subsequently be blanked from the rib cons to provide individual bags as shown in FIGURE 12. Although not shown, recess 42 will preferably have a plurality of ridges which will impress in the bulged side of bag 39 a plurality of creases 45 (see FIGURE 12) for a purpose to be seen.

Bag 33 is adapted to be assembled with housing portion 27a, prior to its securement to housing portion a, in the following manner. Ear portions 46 of bag 39 will be shifted in the direction of the arrows in FIGURE 8 to overlying relation to thus shape the bag to a generally conical configuration with the bulged portion of the bag on the exterior thereof. It is to be understood that creases 45 increase the flexibility of the bag and thus fa cilitate this operation. The bag, in this conical shape, will then be inserted, apex end first, into housing portion 27:: and then released. Upon release of the bag, it will attempt to spring back to its original fiat position but, since it is confined within the housing portion, it will be unable to do so but will merely generally conform to the interior thereof.

Means are provided for insuring against displacement of bag 39 and in the present embodiment, such means comprises a flat, metallic screen 47 which will be forced into housing portion 27a, after the bag has been inserted therein, to force the bag against the inner wall of the housing portion. Screen 47 will, or" course, generally conform to the interior of housing portion 27;: and the normal spring-back of the screen will wedge the latter in position to thus prevent displacement of the bag.

Housing portions 15a, 27a may now be secured together in the same manner as housing portions 15, 27 and the completed housing 13a then filled with dampening liquid through aperture 35a in housing portion 27a and thereafter sealed with cap member 35a. Note that with bag 39 in place in housing portion 27a, the gap between ear portions 46 of the bag provides an opening of which a portion is generally aligned with aperture 35a of housing portion 27a. This permits the air within the housing 13a to escape freely from the interior of the housing through aperture 35:: during filling operations.

In this embodiment, lugs 33 at the curved sides of housing 27 may be omitted from housing 27:: since tl ey serve no function in this construction and the lugs at the top and bottom of the housing portion will preferably be en tended until they blend into the curved rear wall of the housing portion to thereby add stren th to the fiat top and bottom walls of this housing portion.

FIGURE 14 illustrates another embodiment of the invention, similar parts being identified by the same reference characters heretofore used but with the suflix b added. This embodiment employs a kidney-shaped bag 3% which may be identical to bag 3%; however, a somewhat difierent construction is employed to maintain this bag in position within housing portion 27b.

In the embodiment shown in FIGURE 14, the cornpass card supporting member 235 has an upstanding portion 22b to whicr the sleeve (not shown) is secured, a rearwardly extending portion 43, an arcuate upwardly extending portion 49, an upwardly sloped, forwardlyextending portion 5% having an abutment portion 51, a downwardly extending arcuate portion 25b, and a rearwardly extending portion 52. It is to be understood that all of the aforesaid portions normally lie in generally the same plane.

With the parts assembled as shown in FIGURE 14, it will be seen that portion 5d of supporting member sf'b will prevent disassembly of I the compass card therefrom. Assembly of the compass card with the sup porting member, however, may easily be efi'ectuated by springing leg 22b out of the plane of the supporting member, positioning the compass card on the jewel carried by the sleeve, and allowing, or returning, leg 22b to position wherein it is in the same plane as the remainder of the supporting member.

It is to be understood that prior to its assembly with housing portion 15b, the spacing between portions 51, 52 is somewhat greater than the spacing between the grooves 23b, 29b in which they are respectively receivable. Accordingly, supporting member 23b will be sprung into assembled relation with housing portion 15b in the same manner as was disclosed with respect to supporting member 231) and housing portion 15.

Following the assembly of supporting member 231) and its compass card with housing portion 15b, bag 3% will be assembled with housing portion 27b in the same manner as was disclosed with respect to bag 39 and housing portion 27a. Housing portions 15b, 27b may then be secured together in the same manner as was disclosed with respect to housing portions 15, 27. Note that with the housing portions assembled, portion 49 of supportin member 2312 will engage bag 3% and hold it in position within housing portion 271).

It should be pointed out that the construction of supporting member 23b is preferable under certain conditions to that of supporting member 23 for the following reason. Under extreme temperature condi ions, the fiat upper and lower compass card housing walls have been known to bulge outwardly a slight amount. This condition allows supporting member portion 25 to move away from portion 24 and in the event the condition is sufficiently aggravated, portion 25 will no longer ma'ntain the compass card properly assembled with the supporting member in the event the housing is momentarily inverted. When this occurs, the compass becomes useless until housing assembly 13 is replaced by a new one.

It will be noted that with the construction illustrated in FIGURE 14, bulging of the upper and lower housing walls will not increase the clearance between the cornpass card and supporting member portion 59 since such clearance is not maintained, against the resiliency of the supporting member, by the spacing of grooves 28b, 2%. Accordingly, there is no possibility of the compass card becoming disassembled from the supporting member.

In View of the foregoing it will be apparent to those slrilled in the art that l have accomplished at least the principal object of my invention and it will also be apparent to those skilled in the art that the embodiments herein described may be variously changed and modilied, Without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described, hence it will be appreciated that the herein disclosed embodiments are illustrative only, and that my invention is not limited thereto.

I claim:

1. A compass comprising a magnetic body, a supporting member rotatably supporting said body for alignment with the earths magnetic field, a pair of members,

ans "aces a one of which carries said supporting member, secured together to provide a sealed chamber within which said magnetic member is rotatable and filled with liquid to dampen oscillatory movement of said magnetic member, and a flexible Wall container carried by the other of said members for disposition within said chamber and within which a compressible fluid is sealed to provide for temperature caused changes in volume of said liquid, said supporting member being engageable with said container for maintaining the latter in position within said chamber.

2. The construction or claim 1 wherein said supporting member has a part at least partially encircling said magnetic body and wherein such member part is engaged with said container for the purpose aforesaid.

3. The construction of claim 1 wherein said'supporting member has a first part carried by said one member, a second part overlying said magnetic body, and a third part engaged with said container for the purpose aforesaid.

References Cited in the file of this patent UNITED STATES PATENTS Johnson Apr. 22, Lumm Nov. 13, Seward Dec. 4, Chase Feb. 5, Draper et a1. July 8, Moule July 21, Jonsson Dec. 14, Keefer May 23, Krueger Dec. 21,

FOREIGN PATENTS Germany Jan. 9, France Jan. 7, France Aug. 23, Sweden July 11, Belgium July 30, 

1. A COMPASS COMPRISING A MAGNETIC BODY, A SUPPORTING MEMBER ROTATABLY SUPPORTING SAID BODY FOR ALIGNMENT WITH THE EARTH''S MAGNETIC FIELD, A PAIR OF MEMBERS, ONE OF WHICH CARRIES SAID SUPPORTING MEMBER, SECURED TOGETHER TO PROVIDE A SEALED CHAMBER WITHIN WHICH SAID MAGNETIC MEMBER IS ROTATABLE AND FILLED WITH LIQUID TO DAMPEN OSCILLATORY MOVEMENT OF SAID MAGNETIC MEMBER, AND A FLEXIBLE WALL CONTAINER CARRIED BY THE OTHER OF SAID MEMBERS FOR DISPOSITION WITHIN SAID CHAMBER AND WITHIN WHICH A COMPRESSIBLE FLUID IS SEALED TO PROVIDE FOR TEMPERATURE-CAUSED CHANGES IN VOLUME OF SAID LIQUID, SAID SUPPORTING MEMBER BEING ENGAGEABLE WITH SAID CONTAINER FOR MAINTAINING THE LATTER IN POSITION WITHIN SAID CHAMBER. 